Our rec room area has only 1 heating duct that supplies heat to approx. 900 sq. feet of rec room area where we spend time. Even with the heat on most of the day the rec room is at least 10 degrees colder than it is on the main level of our ranch home and we keep our thermostat at 70 degrees all day. Is it possible to open 1 more heating duct in the rec room area so it can be warmer or should we just buy a space heater.

When we bought the home we made the previous owner obtain a permit afor the rec room because he didn't have one when he built the rec room. The city we live in granted the owner the permit after inspection before we purchased the home so we are wondering why is there only 1 heating duct in the rec room? I heard something about there can be so many heating ducts depending on the sq. feet that 1 room can heat based on some type of calculations, maybe I'm wrong.

I would recommend contacting a heating contractor by consulting "Heating Contractors" in the Yellow Pages & get several on-site estimates of how much heat the rec room needs, and more importantly, how it can be "zoned off" from the rest of the house with its own dedicated thermostat, so that you can control the amount of heat in the rec room that will make it comfortable---in a ZONED ROOM a thermostat is installed on the rec room wall that is set to the desired temperature; when the room temp goes below the set temperature, the furnace fires and baffles in the duct work close for the rest of the house & open for the rec room, and heat is supplied only to the rec room until the desired temperature is reached on the rec room thermostat; this system can be expensive to install, so several estimates should be obtained if you want to go this route.

From the photos you have posted, it looks like a rather large area to be heated by only one duct, (there actually should be TWO ducts in the room now; one supply duct to blow in warm air to the rec room, and one RETURN duct, to suck out & return the cooled air back to the furnace to be reheated; the first thing the contractor should do is to make sure the single return/supply ducts are working properly, and that the return duct is also working to suck out & return the cooler air back to the furnace to be re-heated; hold your hand close to the heat supply duct when the furnace is running to feel if warm air is being pumped into the room; hold a piece of tissue paper against the heating supply duct to make sure that it is pumping hot air into the room when the furnace is firing; then look around for the return duct & hold the tissue paper against the return duct to make sure the cooled air is being returned back to the furnace to be reheated.

The calculations you mentioned in your post are based on the square footage of the room, the amount of exterior glass (windows) doors, etc;, and is known as doing a heat loss calculation for the rec room; the square footage of the room is taken and in a basic calculation is multiplied by perhaps 35 btu/square foot/hour, depending on your geographical location, the amount of glass (windows,doors, if any) that are in the room and other factors; thus, for example at 900 square ft. X 35 btu/hr per sq.ft. = 31,500 btu/hour needed to heat the rec room on a cold day; this is based on the assumption that rec rooms are usually sub-grade in a cellar of the house where the warmth of the soil & lack of windows means the rec room requires less heat than an above grade room of similar size; a rec room of 900 sq.ft. is big, and should have its own dedicated zone, so that the furnace can adequately heat the room to a comfortable level; right now, from your post, it sounds like the furnace is trying to heat the whole house from a call from a t-stat on the 1st floor and the rec room is now getting only inadequate auxilary heat, which is not enough to get the rec room comfortable.

I'm assuming from your post that there is currently no room thermostat in the rec room to control the heat output of the furnace for just the rec room (which would be a separate rec room zone); please post back to advise.